1. Field of the Invention
The present invention relates to a package for a high frequency semiconductor device such as a high frequency oscillator (HFO) whose oscillation frequency belongs to, for example, a GHz band. More particularly, the present invention relates to a semiconductor device package, which is designed as a shielding case for surface mounting, for preventing an electromagnetic interference (EMI) and improving a productivity.
2. Description of the Related Art
A high frequency oscillator (HFO) is formed by using a dielectric substance or a strip line and used in, for example, a mobile communications device. In such a high frequency oscillator, an electromagnetic interference (EMI) is easily caused by an electric influence from outside. Therefore, a semiconductor device package is necessary, with which semiconductor devices are encapsulated and shielded.
Japanese Laid Open Utility Model Application (JP-Heisei 1-165650) discloses an IC package including a cover and a ceramic substrate on which an IC is mounted. The cover has tab units which hold opposite side surfaces of the ceramic substrate. Also, this cover has a plurality of pinna sections to be located over the IC.
Japanese Laid Open Utility Model Application (JP-Heisei 3-65299) discloses a shield-package-type circuit device including a ceramic substrate, a ground metal layer, a conductive section, a metal frame, and a shield cap. The ground metal layer is formed in the ceramic substrate. The conductive section is formed on the ceramic substrate and electrically connected to the ground metal layer. The metal frame is formed on the edge of the ceramic substrate and electrically connected to the conductive section. The shield cap for covering devices on the ceramic substrate is fit to the metal frame.
Japanese Laid Open Patent Application (JP-Heisei 5-175351) discloses a semiconductor device package including a radiator metal base, an exterior case attached to the edge of the radiator metal base to form a surrounding outer wall, and a case cover for covering the semiconductor device. Circuit parts and lead terminals are mounted on the radiator metal base. Silicon-gel and epoxy-resin is filled in the exterior case to seal the circuit parts and the lead terminals. The case cover has a rectangular shape. An engagement tab section is provided on one side of the case cover, which is engaged with the exterior case. A protrudent leg section is provided on the opposite side of the one side, which is embedded in the epoxy-resin. Slide tab sections are provided on the other sides of the case cover, which are engaged with edges of the exterior case.
Japanese Laid Open Patent Application (JP-Heisei 8-136771) discloses an optical transmission module which has a receptacle with a convex cross section. This optical transmission module has a cover which can cover that convex receptacle.
Japanese Laid Open Patent Application (JP-Heisei 9-51183) discloses electronic parts including a electronic circuit substrate and a metallic frame on which the electronic circuit substrate is placed. Electronic devices are mounted on the principal surface of the electronic circuit substrate. At least one concave portion is formed on at least one side of the electronic circuit substrate. The metallic frame has a convex portion which is engaged with the concave portion and is used for alignment.
Japanese Laid Open Patent Application (JP-Heisei 10-41665) discloses an oscillator. The oscillator has an insulation substrate, four side electrodes, and a metal cover. The insulation substrate has a rectangular shape, and a ground electrode is formed on a back side of the insulation substrate. The four side electrodes are formed on four sides of the insulation substrate and electrically connected to the ground electrode. The metal cover has four tab units which are formed on four sides of the metal cover and electrically connected to the four side electrodes, respectively. The tab units on opposite sides of the metal cover and the corresponding side electrodes are joined with solder. Each of the tab units on the other opposite sides of the metal cover has a protruded section, and the tab units are strongly engaged with the corresponding side electrodes.
FIGS. 1 to 3 are views explaining one conventional example of such a high frequency semiconductor device package. FIG. 1 is an exploded perspective view of the high frequency semiconductor device package, FIG. 2 is a cross sectional view of the high frequency semiconductor device package, and FIG. 3 is a partially enlarged sectional view of the high frequency semiconductor device package (indicated by a dashed circle). The semiconductor device package 100 has a shielding case composed of a metal cover 101 and a high frequency circuit substrate 103. Also, the semiconductor device package has a device 105 and chip parts 106 accommodated in the shielding case, which constitute an oscillating circuit. The high frequency circuit substrate 103 has a rectangular shape. Ground electrodes 104 are extended into concave portions formed opposite to each other on centers of two sides of the high frequency circuit substrate 103. The metal cover 101 has two tab units 102 which are formed opposite to each other on two sides of the metal cover 101.
As shown in FIG. 3, the tab unit 102 is formed such that its tip is bent in an outer side direction. Those tab units 102 are engaged with the concave portions formed opposite to each other on centers of two sides of the high frequency circuit substrate 103. The metal cover 101 is attached through the engaged portions to the high frequency circuit substrate 3. In this way, the metal cover 101 is attached to the high frequency circuit substrate 103, and the tab units 102 and the ground electrodes 104 are held in contact with each other. Thus, electrical connection is established.
In such a high frequency semiconductor device package, as shown in FIG. 3, the tab unit 102 of the metal cover 101 is bent to form a elbowed shape and a taper 102a is formed at a tip of the elbowed tab unit 102. When trying to attach the metal cover 101 to the high frequency circuit substrate 103, the tab unit 102 is slid to the concave portion by using the taper 102. Thus, the metal cover can be easily attached to the high frequency circuit substrate 103, and the high frequency circuit substrate 103 is put between the tab units 102 of the metal cover 101.
In the above-mentioned high frequency semiconductor device package, the ground electrodes 104 of the high frequency circuit substrate 103 and the tab units 102 of the metal cover 101 are joined. Thus, it is possible to form a shielding case that is almost entirely shielded from outside and to prevent the electromagnetic interference.
However, the conventional high frequency semiconductor device package mentioned above has the following problems.
In the high frequency semiconductor device package mentioned above, the inner wall of the metal cover 101 is the metal surface. Thus, when the inner wall of the metal cover 101 is brought close to the chip parts 106 and devices 105 such as FET mounted on the high frequency circuit substrate 103, the chip parts 106 and the metal cover 101 come into contact with each other. This causes an electric trouble such as a short and the like.
Also, if insulating material is coated on the inner surface of the metal cover 101 and the tab units 102 in order to prevent the above-mentioned trouble, it becomes impossible to electrically connect the tab units 102 and the ground electrodes 104 when attaching the metal cover 101 to the high frequency circuit substrate 103.
Also, an elbowed portion is formed in the tab unit 102 as shown in FIG. 3. Therefore, when sandwiching the high frequency circuit substrate 103 between the tab units 102 of the metal cover 101, the elbowed portion might become located over the upper surface of the high frequency circuit substrate 103 if the thickness of the high frequency circuit substrate 103 is small. This causes slip between the taper 102a of the tab unit 102 and the high frequency circuit substrate 103, which results in problems that the metal cover 101 comes off easily and that the high frequency circuit substrate 103 can not be made thinner.